Polyarylene sulfide resins (hereinafter abbreviated as “PAS resin”), representative examples of which polyphenylene sulfide resins (hereinafter abbreviated as “PPS resin”), are engineering plastics exhibiting excellent heat resistance, chemical resistance, flame retardancy, mechanical strength, characteristics, dimensional stability, and the like. The PAS resin can be formed into various molded products such as films, sheets and fibers by a general melt molding method such as injection molding, extrusion molding or compression molding. Thus, the resin is widely used as a material for resin parts in a wide range of fields including electrical and electric devices, automobile devices and chemical devices.
A known example of a representative method for manufacturing a PAS resin is a method of reacting a sulfur source and a dihalo aromatic compound in an organic amide solvent such as N-methyl-2-pyrrolidone (hereafter abbreviated as “NMP”). A PAS resin obtained by this method typically tends to have a structure in which a halogen bonds to the terminal of a polymer and therefore has a high halogen content, even when sufficiently washed in the separation and recovery step after a polymerization reaction. When such a PAS resin having a high halogen content is used, the corrosion to a metal mold during molding processing as described above or environmental pollution as evidenced by halogen regulations become problems. Further, since the manufacturing conditions of the PAS resin are wide ranging, it is difficult to adjust the conditions. Particularly, it is difficult to achieve a balance between processability or fusion characteristics and burr suppressing characteristics during injection molding. There is a disadvantage in that the amount of burrs generated during injection molding is large. The term “burr” means a portion of a molding material which enters the space between the two parts of a metal mold and solidifies. It is necessary to remove the burr which is solidified into a thin film or flake and attached to a molded product in a finishing step.
In order to reduce the halogen content of the PAS resin, the PAS resin is conventionally washed with high temperature water or an organic solvent in the separation and recovery step after the polymerization reaction. Examples of the organic solvent include the same organic amide solvent as the polymerization solvent, ketones (e.g., acetone) and alcohols (e.g., methanol). Thus, in order to reduce the halogen content of the PAS resin, the halogen content has always been reduced by washing.
On the other hand, a method for adding a branched PAS resin to a linear PAS resin is suggested to suppress generation of burrs during injection molding.
The following has been reported in Japanese Patent No. 5189293: when a branched PAS resin is manufactured by a method including the steps of: reacting a sulfur source with a dihalo aromatic compound in an organic amide solvent; and adding a polyhalo aromatic compound having three or more halogen substituent groups to the polymerization reaction mixture at a predetermined ratio at a stage when the conversion ratio of the dihalo aromatic compound becomes sufficiently high, a branched PAS resin in which all the melt viscosity, average particle size and melt viscoelasticity tan δ are within an appropriate range can be obtained. For example, when the branched PAS resin is blended with a linear PAS resin, an effect as a burr suppressor is exerted and further the surface properties of the molded product are improved.
However, although a PAS resin having a low halogen content and excellent characteristics of suppressing generation of burrs has been earnestly developed, a target resin having such characteristics has not currently been obtained. In the field of the PAS resin, there is a daily increasing demand for the above-described characteristics. The present inventors have developed and studied to satisfy the demand for improvement.